1. Field of the Invention
The invention relates to alignment systems for vehicles and, more particularly, to an alignment system employing a laser beam and an electro-mechanical pendulum.
2. Description of the Prior Art
Prior wheel alignment systems for vehicles have suffered from a variety of drawbacks which have limited their effectiveness. Early wheel alignment systems employed mechanical components such as calibers to measure and adjust steering geometry parameters such as toe-in and toe-out. Mechanical techniques such as these were very cumbersome, difficult to use, and very time-consuming. Among other deficiencies, these techniques could not provide a continuous readout of steering geometry parameters; measurements had to be made with the wheels in one position and separate measurements had to be made with the wheels in other positions. In addition, the difficulty in using these devices often required that a special section of a garage be dedicated exclusively for alignment purposes. Special racks sometimes would be installed permanently for alignment purposes, and these racks could be used for no other purposes than doing vehicle alignment work.
In an attempt to alleviate difficulties associated with mechanical alignment systems, various wheel-mounted optical systems have been developed. Generally speaking, these optical systems project a beam of light to a sensor mounted on one or both front wheels of a vehicle. Unfortunately, these optical systems have been difficult to set-up, and have been unduly complex and expensive. The use of a conventional light beam has led to inaccuracies because the beam undesirably increases in diameter over a relatively short distance. Moreover, prior optical systems have aligned the front wheels of a vehicle by reference to each other, rather than by reference to the chassis of the vehicle. Accordingly, these systems have provided only relative alignment measurements, rather than absolute alignment measurements. In turn, these systems have been unable to take into account mechanical misalignments due to frame damage, bent parts, and the like. Moreover, they have not been able to take into account the effects of sloping or otherwise irregular floors. Accordingly, these systems still require that a special section of a garage be set aside exclusively for vehicle alignment purposes, and special racks still must be used as part of the alignment process.
A particular type of optical alignment system that has had some promise employs a laser beam, rather than a conventional light beam. A laser beam is of interest because a laser beam tends to remain relatively constant in diameter over great distances. Accordingly, the use of a laser beam is desirable because of the accuracy that theoretically is possible by the use of such a beam of light. Unfortunately, the proposed laser beam system has not been entirely successful, in part because a sensor unit employing a photocell has been used. The laser beam impinging on the photocell causes changes in electrical output of the photocell. Depending upon the amount of light striking different portions of the photocell, these changes in electrical output can be correlated to orientation of the wheel relative to the light beam; in turn, readings of steering geometry can be obtained. The most important drawback of this system is that attenuation of the laser beam for any reason influences the output of the photocell and, thus, steering geometry readouts being obtained. For example, airborne dust or other optical attenuators such as cigarette smoke will cause inaccurate readings, thus rendering this proposed system unacceptable under many circumstances.
In view of the difficulties associated with prior wheel alignment systems, there remains a need for an optical alignment system employing the favorable features of a laser beam, without the drawbacks of prior proposals such as undue complexity, expense, lengthy set-up times and the like. Additionally, it is desirable to have a vehicle alignment system that will provide absolute readings of steering geometry, rather than relative readings of steering geometry. Furthermore, it is desirable to have a wheel alignment system that can be used in a great variety of places, and which will not require the use of special racks or sections of a garage.